I have a cast iron dutch oven. It has a self-basting lid, basically it has a grid of little cone shapes on the underside of the lid. The idea is that liquid condenses on underside of the lid and these little cones help the liquid drip back down onto the stuff that is cooking.

I noticed that the tips were a little rusted but I decided to cook a one pot chicken and rice dish in it any way. It the food safe to eat? I couldn't discern any type of rust flavor or anything in the food. I searched around on the web a bit and couldn't really get a straight answer about eating rust. All I've read is that you have to injest quite bit to be of any concern. I think that cooking and eating the food this one time probably won't put my health at risk.

2 Answers
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Just kidding! A little iron in your food isn't going to hurt you, and can actually help prevent anemia. To quote On Food and Cooking (pg 790): "Excess iron is readily eliminated from the body, and most people can actually benefit from additional dietary iron."

Now, to back this up further:

You won't get much iron out of the pan unless you cook something acidic in it. Rust is insoluble in water without acid present, and in order to become soluble you have to convert to iron nitrate, sulfate, or chloride, according to the solubility table. Nothing you cook in there is likely to cause the necessary reactions to render it highly soluble.

I found a source quoting specific numbers for iron from cast iron cookware, if you are concerned. The gist is that most cooking in cast iron added from 1 to 5 mg of iron to the food, with the highest numbers coming from acidic foods with tomatoes. Applesauce was the highest, good for about 7 mg.

This level of iron intake is quite safe and healthy. To give you a point of comparison, the FDA suggests iron intake of 8 mg/day for men, and 18 mg/day for women, and 80% of the world may be iron deficient. Iron toxicity occurs at about 45 mg/day. So, as I initially stated, you're perfectly safe cooking in your cast iron, and are probably helping your health rather than hurting it!

Nice answer. Is it really so difficult to form iron sulfate though? It seems like one egg would have enough sulfur to turn the whole pan into iron sulfate. Is something else required?
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SobachatinaJul 2 '12 at 13:56

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I can confirm having cooked mac 'n cheese in rust-coloured water and feeling fine the next day. Rusty nails and other rusty items of that sort are normally dangerous because of where they've been, not because of the rust.
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Aaronut♦Jul 2 '12 at 14:15

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@Sobachatina: Sulfur in eggs is trapped in the form of cysteine and methionine, so not readily available for inorganic metal salt reactions. However, some small amount of sulfating reactions might account for why eggs do leach a relatively higher amount of iron out of pans.
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BobMcGeeJul 2 '12 at 14:18

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To correct the quote above which says "excess iron is readily excreted from the body", it is actually extremely difficult to excrete excess iron which is why you need to be careful if you're taking dietary iron supplements. There are foods you can eat which bind iron but removing it from the body is a very slow process. The quickest way to excrete iron is through bleeding, which is why women require more dietary iron than men.
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user19831Aug 24 '13 at 15:41